1. Technical Field
This invention relates to an electromagnetic switch operative to close and open an electrical contact arrangement to thereby turn on and off an electrical current flowing through an electrical circuit.
2. Related Art
A known electromagnetic switch, as disclosed in Japanese Patent Application Publication No. 2003-297207, includes an electrical contact arrangement having a pair of fixed contacts and a movable contact, a coil that generates an electromagnetic force when energized, a movable iron core that is movable in a axial direction of the coil, and a resin shaft that transfers a movement of the movable iron core to the movable contact when the electrical contact arrangement is switched from a closed state to an open state.
When the electromagnetic switch is in an OFF state, i.e., when the coil is not in an energized state, the movable iron core is pushed back under influence of a return spring and the movable contact is pressed against an end face of the shaft secured to the movable iron core, so that the movable contact is spaced apart from the pair of fixed contacts, which leads to the open state of the electrical contact arrangement.
When the coil is energized during the open state of the electrical contact arrangement, the movable iron core is attracted into the coil and the movable contact connects or bridges the pair of fixed contacts under influence of a contact pressure spring, which leads to the closed state of the electrical contact arrangement.
In the electromagnetic switch disclosed in Japanese Patent Application Publication No. 2003-297207, as shown in FIG. 7, one axial end side portion of the shaft 120 (a distal end side portion of the shaft relative to the movable contact) is inserted into a shaft insertion hole 110 formed in the movable iron core 100. A periphery of an opening of the shaft insertion hole 110 is plastically deformed inwardly in an inside diameter direction of the hole by a punch 130 pressing against the periphery. An outer periphery of the shaft 120 is pressed against a resultant deformity (referred to as a crimping portion 140) of the movable iron core 100 so that the shaft 120 can be secured to the movable iron core.
However, since an inside diameter of the shaft insertion hole 110 is slightly larger than an outside diameter of the shaft 120, the shaft is in a clearance fit with the hole just before the deformation of the periphery of the opening, i.e., immediately after the one axial end side portion of the shaft 120 is inserted into the shaft insertion hole 110. Accordingly, there is a tendency for the shaft 120 to be secured to the movable iron core in an inclined attitude relative to a center axis of the hole after the deformation of the periphery of the opening.
When the electrical contact arrangement is switched from the closed state to the open state, i.e., when the plunger is pushed back by a reaction force of the return spring after de-energization of the coil, with the shaft 120 being secured to the movable iron core 100 in such an inclined attitude, a proximal corner of the shaft 120 relative to the movable contact first contacts the movable contact and then the entire proximal end face of the shaft 120 is brought into contact with the movable contact when the movable contact is pressed against the shaft 120 at a return position of the movable contact. This gives rise to a bending moment acting on the shaft 120. Since a load caused by the bending moment is intensively applied to the crimping portion 140, the joint between the shaft and the crimping portion 140 is likely to become loose, which may reduce securing capability for securing the shaft 120 to the movable iron core 100.
In consideration of the foregoing, exemplary embodiments of the present invention are directed to providing an electromagnetic switch that can prevent reduction in securing capability for securing a shaft to a movable iron core.